My red HM, Tyrion hates bigger tanks, backgrounds and filters. And he gets lonely. It has been a journey trying to figure out how to keep this one happy. He was happy when I first got him, in a 1 gal hex with no filter. But, after all the "nothing smaller than 2.5 gal" posts on here, I upgraded him to a 3 gal with a filter. He was obviously stressed so I moved him into a divided, NPT 10 gal, on the side without the filter. He chewed big chunks out of his tail. Then moved him into my critter keeper hospital tank (1.5 gal) with no filter and he stopped biting.
Just last week I moved him into a 2.5 gal right next to my monitor at work. He is THRIVING with all the added attention. His tail is growing in already and just seems much calmer. I am in the process of adding live plants for him now that I think I finally found him a permanent home. I am so happy that my little problem child is finally a happy fishy, just like the rest of my herd!